1. Field of the Invention
The present invention relates to a surface acoustic wave device principally for use in a communication device or other electronic apparatus.
2. Description of the Related Art
Hereinafter, a conventional surface acoustic wave device including a surface acoustic wave element and a package is described.
The package includes a main body having an opening and a hollow space therein and a cover for closing the opening of the main body of the package. The main body of the package includes a substrate and at least one frame body provided on the periphery of the substrate. A grounding electrode and signal electrodes are provided on the substrate, and the surface acoustic wave element is fixed in the central portion of the substrate and the electrodes of the surface acoustic wave element are electrically connected to the grounding electrode and the signal electrodes via a metal wire.
The grounding electrode is arranged to connect the vicinity of the middle point of each of a pair of two sides of the substrate that face each other and is in contact with the bottom surface of the surface acoustic wave element. Furthermore, the grounding electrode is arranged so as to continuously cover the outside surface and bottom surface of the package. An unwanted electromagnetic wave generated by the surface acoustic wave element or other source, is absorbed by the grounding electrode. Furthermore, the signal electrodes are extended toward the surface acoustic wave element from the vicinity of the middle point of each of the other pair of two facing sides of the substrate, and the signal electrodes are arranged so as to continuously cover the outside surface and bottom surface of the substrate. The signal electrodes are also located a fixed distance away from the surface acoustic wave element in the vicinity of the surface acoustic wave element on the substrate so as not to contact the grounding electrode. These signal electrodes can input an external signal to the surface acoustic wave element and output a signal from the surface acoustic wave element to the outside.
In order to close the opening portion of the main body of the package, the cover is provided on the upper surface of the frame body. The cover and the frame body are joined by using an insulating joining material such as an insulating adhesive or fused glass, by heat. Then, in the bottom surface of the insulating joining material, that is, the whole area or a part of the upper surface of the frame body, a metallized electrode such as gold, is provided and is arranged to be conductive to the grounding electrode. As a result, an effect of absorbing an unwanted electromagnetic wave generated by the surface acoustic wave element and the signal electrodes can be obtained, and the inside of the package is electrically shielded.
However, the contact between the insulating adhesive or glass used as an insulating joining material and the gold used as a metallized electrode is bad, and as a result, a gap is caused therebetween. Also, there are cases in which the airtight condition of the package cannot be maintained, and also there is a possibility that the moisture penetrated into the gap adversely affects the surface acoustic wave element. When no metallized electrode is provided, the surface acoustic wave device cannot be fully electrically shielded and accordingly, there are cases in which the characteristics of the surface acoustic wave device are worsened.
In order to overcome the problems described above, preferred embodiments of the present invention provide a surface acoustic wave device that is constructed such that when a cover and a frame body are joined, a package including the cover and frame body is sufficiently shielded and the cover is joined to the package without causing any gap therebetween.
A surface acoustic wave device according to a first preferred embodiment of the present invention includes a surface acoustic wave element, and a package containing the surface acoustic wave element, the package including a main body having an opening and a hollow space therein, a cover provided on the upper surface of the main body of the package and arranged to close the opening of the main body of the package, signal electrodes arranged to transmit a signal input from outside of the package and a signal output from the surface acoustic wave element, and a grounding electrode arranged to ground an unwanted electromagnetic wave generated inside the package. The main body of the package and the cover are joined preferably by an insulating joining material, a metallized electrode which is located above the signal electrodes and is not in contact with the signal electrodes and the insulating joining material is provided at a fixed location of the main body of the package, and the metallized electrode is arranged to be conductive to the grounding electrode.
In the surface acoustic wave device according to a first preferred embodiment of the present invention, because no metallized electrode is provided on the surface that is joined by the insulating joining material, a sufficient joining strength can be obtained. Therefore, penetration of moisture into the package is reliably prevented. Furthermore, because the metallized electrode is provided at a fixed location of the main body of the package so as to be located above the signal electrodes and so as not to be in contact with the signal electrodes and the insulating joining material, and is conductive to the grounding electrode such that the grounding electrode absorbs and grounds an unwanted electromagnetic wave, the inside of the package is sufficiently shielded.
A surface acoustic wave device according to a second preferred embodiment of the present invention includes a surface acoustic wave element, and a package containing the surface acoustic wave element, the package including a main body having an opening and a hollow space therein, a cover provided on the upper surface of the main body of the package and arranged to close the opening portion of the main body of the package, signal electrodes arranged to transmit a signal input from outside of the package and a signal output from the surface acoustic wave element, and a grounding electrode for grounding an unwanted electromagnetic wave generated inside the package. The main body of the package and the cover are joined preferably by thermocompression bonding, a metallized electrode is located above the signal electrodes and is not in contact with the signal electrodes, the cover is provided at a fixed location of the main body of the package, and the metallized electrode is conductive to the grounding electrode.
It is preferable that the main body and cover are made of an insulating material.
In the surface acoustic wave device according to the second preferred embodiment of the present invention, even in the case of a surface acoustic wave device in which the cover and the main body of the package which are preferably made of an insulating material are joined by thermocompression bonding, the inside of the package is fully shielded in the same way as in the surface acoustic wave device according to a first preferred embodiment of the present invention.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.